Current development of liquid-repellent surfaces is inspired by the self-cleaning abilities of many natural surfaces on animals, insects, and plants. Water droplets on these natural surfaces roll off or slide off easily, carrying the dirt or insects away with them. The presence of the micro/nanostructures on many of these natural surfaces has been attributed to the water-repellency function. These observations have led to enormous interests in manufacturing biomimetic water-repellent surfaces in the past decade, owing to their broad spectrum of potential applications, ranging from water-repellent fabrics to friction-reduction surfaces.
However, the lotus-leaf-inspired superhydrophobic approach in which liquids are supported by surface textures on a composite solid/air interface, while promising, often suffers from inherent limitations that can severely restrict its applicability. First, trapped air can be a largely ineffective cushion against organic liquids or complex mixtures, which, unlike water, have low surface tension that strongly destabilizes suspended droplets. Moreover, the air trapped within the texture may not stand up against pressure, so that liquids, particularly those with low surface tension, can easily penetrate the texture under even slightly elevated pressures or upon impact, conditions commonly encountered with driving rain or in transport pipes. Furthermore, synthetic textured solids are often prone to irreversible defects arising from mechanical damage and fabrication imperfections; since each defect enhances the likelihood of the droplet pinning and sticking in place, textured surfaces are not only difficult to optimize for liquid mobility but may inevitably stop working over time as irreparable damages accumulate. As a result, foreign material (liquids, dust, oils, ice, microorganisms) can build up within the complex topographical features of superhydrophobic surfaces, making their adhesion even stronger than that of smooth surfaces.
One challenge in the production of slippery surfaces has been to prepare them over large surfaces in a quick and efficient process. An additional challenge has been to identify surface coatings that can remain slippery for long periods of time, particularly when exposed to dynamic flow conditions. A further desirable attribute is the ability to apply slippery coatings readily and securely to a range of underlying surfaces.